CN102906472B - Low friction sealed - Google Patents

Abstract

The invention provides elastic packing, sealing (10) has elastic component (15), elastic component (15) has contact surface (17), for in use contacting active-surface (30), contact surface have on it indenture distribution, indenture have the degree of depth of at least 9 μm, the aspect ratio of at least 0.2 and 0.05 to 0.5 area density.

Description

low friction seal

technical field

The invention relates to the field of seals and bearings. In particular, the present invention relates to low friction seals and methods of making the same.

Background technique

Seals are used to contain leaks between two environments. For example, seals may be used to retain fluids, separate fluids, or prevent the spread of particulate contamination from one environment to another. Static sealing can completely prevent leakage, if the contact surface is very smooth, or if the asperity in the contact is severely deformed and sufficiently flat.

Seals can also be used in non-static devices such as rolling element bearings, or to seal the gap between the shaft and the bore of the bearing frame. An example of a typical elastomeric lip seal is shown in Figure 1. Non-static devices rely on seals to maintain lubrication and prevent the ingress of water, especially particulate contaminants such as sand. They also rely on an extremely thin fluid elastic film on the seal and moving surfaces to prevent excessive wear of the seal, especially at start-up where slow motion causes high friction and seals are most prone to wear.

Sealing is known to account for the friction of major components in sealed bearings. For example, lip seals can account for about 75% of the total bearing power consumption in bearing operation under typical application conditions, which are 1015N (C/P=20) load, 3000rpm speed and grease lubrication. Since hundreds of billions of rubber seals are used worldwide, they run 24 hours a day and 365 days a year, and the total energy consumption of rubber seals is quite huge. Therefore, the reduction in rubber seal-induced frictional torque results in significant energy savings.

Accordingly, it would be desirable for a seal to overcome or at least alleviate some or all of the problems associated with prior art seals, or at least provide a beneficial or optimized alternative.

Contents of the invention

In a first aspect, the invention provides an elastomeric seal, particularly for use in bearings, the seal having a contact surface which, in use, contacts a moving surface, the contact surface having a distribution of indentations thereon, the indentations having A depth of at least 9 μm, an aspect ratio of at least 0.2 and an areal density of 0.05 to 0.5.

According to a second aspect, the present invention provides a method of forming a seal as described herein, the method comprising forming the seal using a mold having on its surface an array of protrusions for forming an array of indentations.

According to a third aspect, the present invention provides a method of forming a seal as described herein, the method comprising forming the seal and using laser engraving to form the array of indentations.

According to a fourth aspect, the invention provides a bearing comprising a seal as described herein.

According to a fifth aspect, the invention provides the use of a seal as herein described to reduce the coefficient of friction in a bearing.

Description of drawings

The invention will now be further described with reference to the accompanying drawings provided by way of example, in which:

Figure 1 shows a partial sectional view of a radial lip seal.

Fig. 2 shows a schematic diagram of how to determine the area density of the dents when the dents are circular and form a regular array. "D" is the diameter of the dents, and "a" is the distance between the centers of the dents forming the repeating unit of the array.

Figure 3 shows a dimple structure on the contact surface showing the elastic seal. The larger scale bar in the upper part of the photograph shows 200 μm. The smaller scale bar in the lower part of the photograph shows 1 mm.

Figures 4a and 4b show histograms of two different circular dimple diameters (D20 and D40) versus non-dimple seals. Both bar graphs have a y-axis showing the reduction (%) in the coefficient of friction. Figure 4a shows the reduction caused by dimples with grease lubrication at a rotational speed of 1000 rpm. Figure 4b shows the reduction caused by dimples with grease lubrication at a rotational speed of 50 rpm.

Figures 5a and 5b show histograms of the coefficient of friction [μ] in seals at different rotational speeds (rpm). Figure 5a shows the effect of a grease lubricant (LGMT2). Figure 5b shows the effect of an oil lubricant (oil-based LGMT2). The left-hand dark bars show sealing with a dent of 40 μm (D40) diameter at each speed. The right-hand light bar shows the non-dent seal (base-line) at each speed. The values on each pair of bars show the reduction in the coefficient of friction obtained by the addition of indentations.

Figure 6 shows the reduction in coefficient of friction (%) for different dimple diameters (μm) D20, D40 and D60 relative to non-dimpled seals. Different lines represent different rotational speeds. On D20, the reduction is greatest at 50rpm, then 1000rpm, then 200rpm and the smallest reduction at 500rpm.

detailed description

The invention is now further described. In the following sections, different aspects/embodiments of the invention are defined in more detail. Each aspect/embodiment so defined may be combined with any other aspect/embodiment or aspects/embodiments unless indicated to the contrary. In particular, any feature indicated as preferred or advantageous may be combined with any other plurality of features indicated as preferred or advantageous.

In a first aspect, the present invention provides a resilient seal, such as a radial lip seal, for dynamic applications. The seal can be installed between the inner and outer rings of rolling element bearings. Alternatively, as shown in the example of FIG. 1 , the seal 10 may surround the gap between the housing 20 and the shaft 30 . Typically, the seal comprises a metal housing 12 engaged with a resilient sealing lip 15 . The sealing lip has a contact surface 17 which bears against an opposite face on the shaft 30 . To ensure that the lip 15 remains in contact with the shaft 30 , the seal in this example is provided with an annular helical spring 18 . During use of the seal, the sealing lip 15 is in sliding contact with the shaft. To reduce friction, the sliding contacts are lubricated with oil or a base oil from grease. In the seal according to the invention, the friction is further reduced in that the contact surface 17 on the sealing lip 15 is provided with a distribution of indentations. The dimples have a depth of at least 9 μm, an aspect ratio of at least 0.2 and an areal density of 0.05 to 0.5.

Frictional torque in a dynamic sealing arrangement is primarily generated by the frictional sliding contact between the rubber sealing lip and the opposing surface, usually the surface of a steel shaft or bearing ring. The inventors have found that the dimpled surface structures described herein provide a significant reduction in seal friction under oil and grease lubrication; especially grease lubrication. Additionally, they have optimized the dimple size of the seal structure to provide a beneficial low-friction seal.

A "dimple" as discussed herein refers to a small indentation or indentation in the surface of the seal. A dimple is a small, shallow indentation in a surface relative to the size of the seal. The dimples may have any shape or profile on the sealing surface and extend into the seal. In one embodiment, the shape and arrangement of the dimples may resemble the surface structure of a golf ball on which the seal is provided with a distribution of indentations.

Dimples have a different surface structure than posts or bumps. The inventors have found that this dimple structure surprisingly has an improved sealing friction effect compared to eg a pillar type structure. The post changes the pumpability of the seal, ie reduces the "reverse" suction effect. However, the inventors have found that the use of the dimples described herein has no effect on the suction effect.

Also, dents are very different from mere surface roughness. The dimples are deep and are specifically placed on the surface to provide a beneficial effect. Plus, dents are very different from ruts, grooves, or surface scratches. The shape, size and placement of the dimples are critical to providing a friction-reducing seal.

The indentations have a depth of at least 9 μm. The depth of the dent is measured from the lowest point in the dent to the flush surface of the seal. Measurements are made along a line perpendicular to the sealing surface. Techniques for observing and measuring surface parameters are known. Therefore, the depth, size and distribution parameters of the indentations on the surface are determined with these techniques.

Preferably, the dimples have a depth of 9 to 15 μm. Preferably, the dimples have a depth of 10 to 12 μm. Dimples with a depth greater than 15 μm were surprisingly found to reduce the positive effect of seal friction. It may further be speculated that the deeper the recessed surface, the greater the tendency to wear. It has been found that process limitations make it difficult to produce smaller dimples without undue cost, and that the benefit diminishes as the dimples become smaller and approach the value of surface roughness.

The dimples are preferably all of substantially the same size, but at least the parameter average of the dimples should preferably satisfy the parameters described herein. That is, preferably, the dimples have an average depth of at least 9 μm, an average aspect ratio of at least 0.2, and an average area density of 0.05 to 0.5. The standard deviation of each parameter from the mean is preferably low, for example, the standard deviation from the mean depth is preferably less than 0.25 μm, the mean aspect ratio is preferably less than 0.025, and the mean areal density is less than 0.0025.

The dimples have an area density of 0.1 to 0.3, preferably 0.15 to 0.25. Preferably, the areal density is from 0.18 to 0.22, most preferably about 0.20. Area density is a measure of the extent to which dimples cover the contact surface 17 of the seal. Area density is calculated by determining the ratio of indentations to total area in the smallest repeating unit of the surface. For example, in a regular square grid array, as shown in Figure 2, the area density - or indentation fraction f - can be calculated as follows: πr ² /a ² . Using diameter, the sag fraction can be calculated as f=ΠD ² /4a ² .

The dimples have an aspect ratio of at least 0.2. The aspect ratio is the ratio of the dimple depth to the dimple diameter. For non-circular dents, the aspect ratio can be determined using the average diameter from the preceding formula. Preferably, the aspect ratio is from 0.2 to 0.75, more preferably from 0.25 to 0.5. These aspect ratios have been found to provide a beneficial reduction in seal friction without undue wear.

Preferably, each indentation presents a substantially circular cross-section on the contact surface. Alternatively, the surface cross-section may be elongated in one direction to provide an elliptical cross-section. Especially when the dimples are circular at the contact surface, the dimples preferably have a diameter of 20 to 40 μm (D20 to D40) on the contact surface. Usually the lip contact width of the rubber seal is small (less than 1mm). The inventors have found that smaller dimples are preferred. Without wishing to be bound by theory, it is speculated that this allows for a maximum amount of dimples on the lip contacting surface. In this case, D20 and D40 were chosen for dent sealing.

Preferably, the dimples are cylindrical, conical or frusto-conical. That is, the dimple volume is preferably cylindrical, conical or frusto-conical in shape. Most preferred dimples have a substantially circular cross-section extending through the seal. The cross-section may be conical, whether point or substantially circular base. Preferably, the dimples are cylindrical, or have a slightly conical shape. These shapes are the easiest to form with moulds, and thus reduce the cost of producing the sealing surface structure.

Preferably, the distribution of indentations forms a regular array. For example, the indentations may be arranged in a regular grid, or in a hexagonal envelope configuration. Other configurations or distributions can be selected as desired.

Preferably, the array of indentations covers substantially the entire contact surface. This obviously adds to the beneficial effect. Furthermore, the dimples may extend beyond the contact surface on the seal for ease of manufacture.

The elastic seal, in particular the sealing lip, is preferably formed from a deformable elastomer. Seals can be reinforced by springs or stretch/elastic components. Preferred elastomers for the seal include acrylic rubber, fluororubber, nitrile rubber, hydrogenated nitrile rubber, or a blend of two or more thereof.

The seal is preferably a lip seal. Lip seals and the construction of such seals are known in the art. The seal has a contact surface for contact with the active surface in use and this forms part of the sealing lip. The active surface (opposite surface) is the surface with which the seal operates, and is not particularly limited. For example, the opposing surface may be the surface of a rotating shaft or a rotatable bearing ring in a rolling element bearing. The opposing faces comprise any suitable material depending on the application and strength requirements. For example, plastic, composite or metallic substances may be used.

Preferably, the contact surface of the sealing lip is provided with a wear-resistant coating. Such coatings are known for lip seals. Preferably, the coating is provided after surface texturing to ensure that the coating lines the dents. It is preferred that the thickness of the coating be considered during dimple preparation to ensure that the final dimple including the wear resistant coating is uniform as described herein.

In a second aspect, the present invention provides a method of forming the seal described herein, the method comprising forming the seal using a mold having an array of protrusions on one surface thereof for forming an array of indentations on the contact surface of the sealing lip .

In a third aspect, the invention provides a method of forming a seal as described herein, the method comprising forming a seal and using laser engraving to form an array of indentations.

In a fourth aspect, the invention provides a bearing comprising a seal as described herein.

Preferably, the bearing also includes a grease lubricant. The inventors have found that the surface dimples described herein are particularly effective in reducing the coefficient of friction when grease lubricants are used for sealing.

In a fifth aspect, the invention provides the use of a seal as described herein to reduce the coefficient of friction in a bearing.

example

The effectiveness of the invention is demonstrated by the following non-limiting examples.

A dimple structure was prepared on the sealing lip and a textured seal was tested. Dimples were prepared by laser technology to have dimples with diameters of 20 μm (D20), 40 μm (D40) and 60 μm (D60). The D20 and D40 dimples have a depth of 9 microns. The D60 indents have a depth of 10 microns. All dimples have an area density of 0.20 (20%). The dimpled structure D40 (diameter 40 μm) provides the highest coefficient of friction reduction. Two samples were prepared and tested for each dimple size.

The surface structures were produced with a Nd:YV04 laser operating at a wavelength of 355 nm in the exasecond pulse range (10x10 ^-12 s). Since the laser operates in the UV range (10 to 400nm) and has very short pulses, it provides very well defined structures (clearly textured surfaces) in the absence of molten debris.

Then, test the textured seal on the seal test equipment (ERCPearlIIrig), lubricated with LGMT2 grease and base oil of LGMT2 grease, at speeds of 50rpm, 200rpm, 500rpm and 1000rpm, on a standard steel shaft Ra0.45μm, where the shaft diameter is 82mm. The linear sliding speeds of the sealing lips on the shaft surface are 0.215m/s, 0.859, 2.147 and 4.294m/s, respectively. Friction torque was measured during the test and the coefficient of friction was calculated from the radial force of the seal on the shaft measured before the test.

The effect of shaft speed on seal friction was observed: seal friction increased with increasing shaft speed from 50 rpm to 200 rpm and/or 500 rpm and then decreased over 1000 rpm. With few exceptions, there is a tendency that the dimples are slightly less effective in reducing seal friction for oil and grease lubricated conditions as shaft speed increases. Without wishing to be bound by theory, as the shaft speed increases, the hydraulic lubrication effect and lubricating film thickness increase. As a result, the contribution of the surface structure to building the film and the reduction in seal friction is reduced.

Figure 6 shows the reduction in coefficient of friction (%) over different dimple diameters (μm) D20, D40 and D60 compared to non-dimpled seals lubricated with LGMT2 grease. Different lines represent different rotation speeds. The D40 notch shows the greatest reduction in coefficient of friction at all speeds. It also works best at slow (50rpm) spin speeds.

Under LGMT2 grease lubrication, the highest reduction in friction was obtained with D40 and D20 (7 to 16% reduction). Figures 4a and 4b show a larger reduction (vs. D40) as a different baseline (non-dimple seal) is used.

When referring to elements of the invention or its preferred embodiments, the articles "a", "the" and "said" are intended to mean that there are one or more of the elements. The words "comprising," "comprising," and "having" are intended to be inclusive and mean additional elements other than the listed elements.

The foregoing detailed description has been provided by way of illustration and example, and is not meant to limit the scope of the appended claims. Those of ordinary skill in the art will recognize many variations from the preferred embodiments shown herein which fall within the scope of the appended claims and their equivalents.

Claims (16)

1. A seal (10) comprising a resilient member (15) having a contact surface (17) for contacting a movable surface (30) in use, the contact surface having an indentation thereon distribution, the indentations have a height of 9 to 15 μm, an aspect ratio of at least 0.2 and an area density of 0.10 to 0.30. 2. The seal of claim 1, wherein the distribution of dimples forms a regular array. 3. The seal of claim 2, wherein the array of indentations covers substantially the entire contact surface. 4. The seal of claim 2, wherein the indentation presents a substantially circular cross-section at the contact surface. 5. The seal according to claim 4, wherein the dimple has a diameter at the contact surface of from 20 to 40 μm. 6. The seal according to claim 4 or 5, wherein the indentation is cylindrical, conical. 7. The seal of claim 6, wherein the cone is a frusto-cone. 8. The seal of claim 1, wherein the aspect ratio of the dimple is 0.25 to 0.5. 9. The seal of claim 1, wherein the areal density is 0.18 to 0.22. 10. A seal according to claim 1, wherein the contact surface is provided with an abrasion resistant coating. 11. The seal of claim 1, wherein the seal is a radial lip seal. 12. A method of forming a seal according to any one of the preceding claims, the method comprising forming the resilient member (15) using a mold having an array of protrusions on its surface for forming the resilient member (15) ) on the contact surface (17) to form an array of indentations. 13. A method of forming a seal according to any one of claims 1 to 11, the method comprising using laser engraving to form an array of indentations on the contact surface (17) of the resilient member (15). 14. A bearing comprising a seal according to any one of claims 1 to 11. 15. The bearing of claim 14, further comprising a grease lubricant. 16. Use of a seal according to any one of claims 1 to 11 to reduce the coefficient of friction in a bearing.